Golf is enjoyed by a wide variety of players—players of different genders, and players of dramatically different ages and skill levels. Golf is somewhat unique in the sporting world in that such diverse collections of players can play together in golf outings or events, even in direct competition with one another (e.g., using handicapped scoring, different tee boxes, etc.), and still enjoy the golf outing or competition. These factors, together with increased golf programming on television (e.g., golf tournaments, golf news, golf history, and/or other golf programming) and the rise of well known golf superstars, at least in part, have increased golfs popularity in recent years, both in the United States and across the world.
Golfers at all skill levels seek to improve their performance, lower their golf scores, and reach that next performance “level.” Manufacturers of all types of golf equipment have responded to these demands, and recent years have seen dramatic changes and improvements in golf equipment. For example, a wide range of different golf ball models now are available, with some balls designed to fly farther and straighter, provide higher or flatter trajectory, provide more spin, control, and feel (particularly around the greens), etc.
Being the sole instrument that sets a golf ball in motion during play, the golf club also has been the subject of much technological research and advancement in recent years. For example, the market has seen improvements in golf club heads, shafts, and grips in recent years. Additionally, other technological advancements have been made in an effort to better match the various elements of the golf club and characteristics of a golf ball to a particular user's swing features or characteristics (e.g., club fitting technology, ball launch angle measurement technology, etc.).
Despite the various technological improvements, golf remains a difficult game to play at a high level. For a golf ball to reliably fly straight and in the desired direction, a golf club must meet the golf ball square (or substantially square) to the desired target path. Moreover, the golf club must meet the golf ball at or close to a desired location on the club head face (i.e., on or near a “desired” or “optimal” ball contact location) to reliably fly straight, in the desired direction, and for a desired distance. Off-center hits may tend to “twist” the club face when it contacts the ball, thereby sending the ball in the wrong direction, imparting undesired hook or slice spin, and/or robbing the shot of distance. Club face/ball contact that deviates from squared contact and/or is located away from the club's desired ball contact location, even by a relatively minor amount, also can launch the golf ball in the wrong direction, often with undesired hook or slice spin, and/or can rob the shot of distance. Accordingly, club head features that can help a user keep the club face square with the ball would tend to help the ball fly straighter and truer, in the desired direction, and often with improved and/or reliable distance.
Various golf club heads have been designed to improve a golfer's accuracy by assisting the golfer in squaring the club head face at impact with a golf ball. A number of golf club heads reposition the weight of the golf club head in order to alter the location of the club head's center of gravity. The location of the center of gravity of the golf club head is one factor that determines whether a golf ball is propelled in the intended direction. When the center of gravity is positioned behind the point of engagement on the contact surface, the golf ball follows a generally straight route. When the center of gravity is spaced to a side of the point of engagement, however, the golf ball may fly in an unintended direction and/or may follow a route that curves left or right, ball flights that are often referred to as “pulls,” “pushes,” “draws,” “fades,” “hooks,” or “slices”. Similarly, when the center of gravity is spaced above or below the point of engagement, the route of the golf ball may exhibit more boring or climbing trajectories, respectively. In some circumstances, it may be desirable to raise or lower the center of gravity of a club head in order to achieve these and other ball flight characteristics.
The degree of twisting of the club head upon off-center impacts can also be dependent upon the moment of inertia of the club head. Generally, a higher moment of inertia results in less twisting of the club head on impact. The moment of inertia can be increased by distributing the weight of the club head proportionally more toward the edges of the head and away from the center or location of contact.
Many off-center golf hits are caused by common errors in swinging the golf club that are committed repeatedly by the golfer, and which may be similarly committed by many other golfers. As a result, patterns can often be detected, where a large percentage of off-center hits occur in certain areas of the club face. For example, one such pattern that has been detected is that many high handicap golfers tend to hit the ball on the low-heel area of the club face and/or on the high-toe area of the club face. Other golfers may tend to miss in other areas of the club face. Because golf clubs are typically designed to contact the ball at or around the center of the face, such off-center hits may result in less energy being transferred to the ball, decreasing the distance of the shot. The energy or velocity transferred to the ball by a golf club can be expressed using a measurement called “coefficient of restitution” (or “COR”). The maximum COR for golf club heads is currently limited by the USGA at 0.83. As described above, the direction of ball flight and the degree of twisting of the club head during impact may also be related, at least in part, to the moment of inertia of the club head and the location of the center of gravity of the club head with relation to the point of impact. The energy or velocity transferred to the ball by the golf club may also be related to the moment of inertia and/or the location of the center of gravity of the club head.
The distance and direction of ball flight can also be significantly affected by the spin imparted to the ball by the impact with the club head. While the ball is in the air, aerodynamic forces caused by the speed and direction of ball spin can cause the trajectory of the ball to be higher or lower, or to curve, and create “draws,” “fades,” “hooks,” “slices,” etc. Additionally, the spin of the ball can change the behavior of the ball as it rolls and bounces after impact with the ground. For example, a high degree of backspin can cause the ball to slow, stop, or even roll backward upon impact, and conversely, topspin or lesser degrees of backspin will cause the ball to travel a greater distance after impact with the ground. Various speeds and directions of spin on the ball can be a product of many factors, including the point of impact, the direction of the club head upon impact, the degree of twisting of the club head upon impact, and the location of the center of gravity of the club head.
Accordingly, a need exists to customize or adjust the moment of inertia and/or the location of the center of gravity of a golf club head to provide maximum energy transfer and minimum twisting during impacts on the face, as well as to provide desired ball flight characteristics after impact.